Method for producing a compact catalytic reactor

ABSTRACT

A process for producing a compact catalytic reactor, in which reaction spaces or heat-transfer spaces are formed by stacking at least partially structured plates alternately one on top of the other, a catalyst is introduced into the reaction spaces, and the plates are provided with a layer of solder at least in the edge region, but not in the region provided with catalyst material, and, after stacking them one on top of the other, are soldered to form a reactor. In addition, the plates may be provided with a bent-up edge region a for easy positioning and for increasing the leak tightness. Finally, an unstructured intermediate plate may also be respectively provided between the structured plates.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of PCT International PatentApplication No. PCT/EP99/03737, filed May 29, 1999 (29.05.99) and Germanpatent document 198 25 102.5, filed Jun. 5, 1998 (05.06.98), thedisclosure of which is expressly incorporated by reference herein.

The invention relates to a process for making a compact catalyticreactor.

Such compact catalytic reactors, so-called micro-reactors, compriseindividual thin, finely structured plates or sheets, in which thestructuring provides fine flow channels for the distribution of therequired media. The sheets are stacked one on top of the other and areprovided with bottom and top plates as well as with supply and dischargeducts for the media, so that a compact component is produced. The sheetsare subsequently joined together in a gastight manner, preferably bydiffusion welding. International patent document WO 88/06941 discloses,for example, a micro heat exchanger of microstructured sheets, which isjoined together by soldering.

It is an object of the invention to provide a simple and inexpensiveprocess for making a compact catalytic reactor of this type.

This and other objects and advantages are achieved by the manufacturingaccording to the invention, which provides a compact catalytic reactorwith adequate leak tightness and mechanical strength. Since a layer ofsolder is provided on all the plates, at least in the edge region,neighboring plates are connected to one another in a gastight manner bythe soldering operation, at least in this edge region, so thatclosed-off reaction or heat-transfer spaces form between respectiveneighboring plates. At the same time, a layer of solder is notintroduced in the regions of the plates in which catalyst material isprovided. As a result, damage to the catalyst material by the soldermaterial can be avoided.

The strength in the region of the plates which is provided with catalystis established exclusively by mechanical contact. If, in addition, allthe plates which have no catalyst material are provided completely witha layer of solder, soldered connections are also produced in the centralregions of these plates, so that the mechanical strength of the reactorcan be further improved.

The bending up of the edge regions allows the plates to be positioned ina simple way during stacking one on top of the other and to be fixedduring the soldering operation. At the same time, leak tightness isimproved.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a basic representation of a reactor to be produced accordingto the invention;

FIG. 2 shows a further refinement of a reactor to be produced accordingto the invention; and

FIG. 3 shows a further exemplary embodiment of a reactor to be producedaccording to the invention, with intermediate layers;

FIG. 4 shows a fourth exemplary embodiment of a reactor to be producedaccording to the invention, with intermediate layers; and

FIG. 5 shows a fifth exemplary embodiment of a reactor producedaccording to the invention, with corrugated sheets.

DETAILED DESCRIPTION OF THE DRAWINGS

The structure of catalytic reactors in plate form is generally knownfrom the prior art and is therefore explained here only briefly withreference to FIG. 1. The catalytic reactor 1 is constructed by stackingplates, preferably in the form of metal foils 2 a-2 c, one on top of theother. The metal foils 2 a-2 c have microstructures worked into at leastpart of the surface, for example in the form of channels 3, which servefor better distribution of the reaction media involved. By stacking themetal foils 2 a-2 c one on top of the other, a reaction space 5,provided with a catalyst material 4, and a heat-transfer space 6, flowedthrough by a heat-transfer medium, are formed between the individualmetal foils 2 a-2 c. The stack of metal foils 2 a-2 c is respectivelyclosed off in the stacking direction by end plates (not shown) . Supplyof the reaction media may take place in any desired form inside oroutside the stack of plates, preferably through supply and dischargechannels, which extend in the stacking direction. These are formed bycorresponding bores in the metal foils 2 a-2 c but are not representedfor the sake of simplicity. The supply and discharge of the reactionmedia to and from these supply channels takes place via the end plates.

In principle, such a catalytic reactor 1 has the function of dischargingthermal energy from the reaction space 5 via a heat-transfer medium(exothermic reaction) or introducing it into the reaction space 5(endothermic reaction). (A thermal oil may be used for example as theheat-transfer medium.) In the case of endothermic reactions, it is alsopossible, however, to generate the thermal energy required directly inthe heat-transfer space 6. For this purpose, a chemical fuel isintroduced into the heat-transfer space 6 as a heat-transfer medium andis oxidized there with the aid of a suitable catalyst and the additionof oxygen. For this purpose, platinum-containing catalysts may be usedfor example. The energy released during the oxidation is transferred tothe reaction space 5. The catalyst material 4 may be introduced into thereaction space 5 in any desired form, for example as a loose fill orpellets, but also by coating the metal foils.

Various reactions may take place in the reaction space 5. For example, ahydrogen-rich gas can be produced there from a hydrocarbon-containingfuel by water vapor reforming and/or partial oxidation. Furthermore,carbon monoxide contained in a hydrogen-rich gas can be removed there byselective oxidation. Finally, a fuel may be oxidized as completely aspossible in the reaction space 5 (catalytic burner), the thermal energyreleased either being transferred to a heat-transfer medium or useddirectly for vaporizing a liquid medium. Such catalytic reactors arepreferably used in so-called gas generating systems for mobile fuel cellapplications, the hydrogen required for the fuel cell being generated inthese gas generating systems from a fuel, for example methanol. It goeswithout saying that a catalytic reactor 1 produced according to theinvention can, however, also be used for any other desired applications.

In the production of the catalytic reactor 1, the individual metal foils2 a-2 c are connected to one another in a gastight manner by soldering.For this purpose, a layer of solder 7 is to introduced betweenrespective neighboring metal foils 2 a-2 c. This layer of solder 7extends at least over the edge region 8 of the metal foils 2 a-2 c. Itmay be introduced in the form of a soldering foil or by coating theupper side and/or underside of the metal foils 2 a-2 c. In the reactionspace 5, the layer of solder 7 is removed in the region in which thecatalyst material 4 is arranged. It therefore has a correspondingclearance 10, which is made for example by punching into the layer ofsolder 7. If the supply and discharge of the reaction media takes placeas described above via supply channels running in the stackingdirection, the circumference of some of the bores is likewise providedwith a layer of solder 7. If a bore is provided with a layer of solder7, the corresponding supply line is sealed off with respect to theassociated reaction space 5 or heat-transfer space 6 after assembly. Ifa bore is not surrounded with a layer of solder 7, an exchange of themedia can take place between the supply line and the associated reactionspace 5 or heat-transfer space 6.

For producing the catalytic reactor 1, vacuum or inert-gas solderingprocesses known per se may be used, for example, the individual plates 2a-2 c being soldered to one another by pressure and temperature. Work iscarried out here, for example, at a temperature of 700°-1200° C.However, the temperature must be chosen such that the catalyst material4 used is not damaged. A platinum-containing noble metal catalyst on anAl₂O₃ carrier material may be used for example as the catalyst material4. The metal foils 2 a-2 c preferably consist of Cr—Ni steel with athickness of 0.3-0.5 mm. The plates 2 a-2 c may, however, also consistof some other material suitable for this intended use. The layer ofsolder 7, preferably in the form of a copper or nickel solder, isoptimized for the vacuum soldering process and preferably has athickness of 30-100 mm. If the layer of solder 7 is applied by coatingthe plates 2 a-c, the layer preferably has a thickness of 10-40 mm. Toprevent soldering material from coming into contact with the catalystmaterial 4 during the soldering operation, in the region of the reactionspace 5 the layer of solder 7 is merely provided in the edge region 8 ofthe metal foils. This is because the catalyst material 4 could bedestroyed, or at least impaired in its function, by contact with thesoldering material.

The exemplary embodiment represented in FIG. 1 shows an example of thestructure of a catalytic reactor 1 made by the process according to theinvention, with three metal foils 2 a 2 c. In reality, a catalyticreactor 1 generally has a multiplicity of such metal foils 2 a-2 c andis respectively bounded by end plates. In FIG. 1, all the metal foils 2a-2 c are provided on the upper side with channels 3. After joining themtogether, a heat-transfer space 6 forms between the metal foils 2 a and2 b. The channels 3 made in the metal foil 2 c are filled at leastpartially with a catalyst material 4 or are correspondingly coated.Therefore, after joining them together, a reaction space 5 forms betweenthe two metal foils 2 b and 2 c. While between the metal foils 2 a and 2b (that is, in the region of the heat-transfer space 6) a continuoussoldering foil 7 is provided, the corresponding soldering foil 7 betweenthe metal foils 2 b and 2 c (in the region of the reaction space 5)extends only over the edge region 8. If the layer of solder 7 isintroduced in the form of a soldering foil, the soldering foil iscorrespondingly punched out. If the layer of solder 7 is applied bycoating, a covering is arranged in the region later provided withcatalyst material 4. This covering can then be removed before joiningthe metal foils together, so that there is no layer of solder 7 in theregion of the reaction space 5 provided with catalyst material 4.

In the exemplary embodiments, the channels 3 are all represented asequidistant and with the same cross section for the sake of simplicity.In reality, these channels 3 may be made in the metal foils 2 a-2 c inany desired arrangement and with variable cross sections. In particular,relatively large contiguous depressions may also be provided. Afterassembly, the reaction media can then be introduced in the same oropposite directions in relation to one another, or transversely.

As a departure from FIG. 1, the metal foils 2 a-2 c in the exemplaryembodiment according to FIG. 2 have a bent-up edge region 11. Otherwise,the same parts are identified by corresponding reference numerals. Thebending over of the edge regions 11, which preferably takes place beforethe stacking of the metal foils 2 a-2 c one on top of the other, givesthe metal foils 2 a-2 c a kind of pan shape. As a result, the metalfoils 2 a-2 c are automatically positioned with respect to one anotherduring stacking one on top of the other, and the leak tightness of thearrangement is improved as well. In this exemplary embodiment, too, thelayer of solder 7 may be introduced in the form of a soldering foil orby coating the metal foils 2 a-2 c.

In the catalytic reactors 1 according to FIGS. 3 and 4, unstructuredintermediate plates 9 are added between the individual structured metalfoils 2 a-2 c. As a departure from FIGS. 1 and 2, the metal foils 2 a-2c have channels 3 on both sides. The respective upper channels 3 form areaction space 5 in interaction with the neighboring intermediate plates9, and the respective lower channels 3 correspondingly form aheat-transfer space 6. The intermediate plate 9 is therefore provided onthe upper side (the surface facing the heat-transfer space 6) completelywith a layer of solder 7, while the layer of solder 7 on the underside(the surface facing the reaction space 5) has a clearance 10.Consequently, in this arrangement with the intermediate plate 9 as well,the catalyst material 4 in the reaction space 5 does not come intocontact with the layer of solder 7. Of course, it is apparent that thearrangement of the reaction space 5 or of the heat-transfer space 6 mayalso be changed over, with one in the place of the other. Furthermore,the spaces 5, 6 do not have to be arranged in the sequence represented.Rather, the sequence can be freely chosen. It is also possible toprovide reaction spaces 5 or heat-transfer spaces 6 in a metal foil 2a-2 c respectively on both sides.

In principle, the claimed production process provides a catalyticreactor 1 in which the individual metal foils 2 a-2 c are connected toone another in a secure and gastight manner, at least in the edge region8, 11, by a soldered connection. Secure soldered connections are alsoobtained in the region of the heat-transfer spaces 6 between theelevations in the heat-transfer space 6 and the unstructured surface ofthe neighboring metal foil 2 a-2 c or intermediate plate 9. In theregion of the reaction spaces 5, however, only mechanical connectionsare obtained. However, in combination with the existing solderedconnections, these are adequate for the required load-bearing capacityof the catalytic reactors 1.

In the exemplary embodiment according to FIG. 4, the intermediate plates9 also have a bent-up edge region 11. Under certain circumstances, it isdesirable to provide a defined gap between the structured surfaces ofthe metal foils 2 a-2 c and the unstructured surfaces of theneighbouring metal foil 2 a-2 c or intermediate plates 9 in the regionof the reaction space 5 and/or the heat-transfer space 6. In this case,an intermediate plate 9 which has corresponding depressions orclearances 10 over the entire region or else only a partial region ofthe reaction space 5 and/or the heat-transfer space 6 is used.Consequently, reaction spaces 5 and/or heat-transfer spaces 6 can beformed with a defined gap in a simple way.

FIG. 5 shows such an example, in which the same parts again areidentified by the same reference numerals. As a departure from theprevious exemplary embodiments, in this case metal foils provided withstructures are not used as plates 2 a-2 c, but instead corrugated sheetsare used. The channels 3 are therefore formed by the corrugations of thesheets 2 a-2 c. In FIG. 4, the sequence of the individual componentparts, and possibly also of the spaces 5, 6, likewise differs from theabove exemplary embodiments. The structuring of the sheets 2 a-2 c ispreferably configured in such a way that the corrugations of successivesheets do not run congruently but intersect. Therefore, during assembly,successive sheets are not pushed one into the other, but instead acorrugation trough of one sheet is respectively in contact with acorrugation crest of the next sheet, so that only punctiform solderedconnections are produced.

The catalyst material 4 is introduced into the reaction space 5 bycoating the sheets 2 b, 2 c. In this case, only the surfaces of thesheets 2 b, 2 c respectively facing the reaction space 5 are coated. Inthe exemplary embodiment according to FIG. 5, this means that theunderside of the sheet 2 a and the upper side of the sheet 2 b in theregion of the reaction space 5 are coated with catalyst material 4. Thetwo sheets 2 a, arranged right at the top and right at the bottom in theexemplary embodiment, and the edge regions 11 of all the sheets 2 a-2 c,are not coated with catalyst material 4. Consequently, heat-transferspaces 6 are formed between the sheets 2 a and 2 b or between 2 c and 2a. In the exemplary embodiment, a layer of solder 7 is respectivelyprovided between the sheets 2 a and 2 b or between 2 c and 2 a, so thatafter the soldering process—during which the solder collects at thepoints of contact of the sheets—a respective single continuousheat-transfer space 6 forms. However, instead of this, it is alsopossible to provide an intermediate plate 9 having a layer of solder onboth sides, so that then two successive heat-transfer spaces 6 wouldrespectively form.

An intermediate plate 9 having a layer of solder 7 on both sides isprovided between the two sheets 2 b and 2 c provided with catalystmaterial 4. This intermediate plate 9 has a clearance 10 in the regionof the reaction space 5. As a result, a defined gap is formed betweenthe sheets 2 b and 2 c. It would also be possible, however, to replacethe intermediate plates 9 coated with solder by a corresponding simplelayer of solder 7. In this case, such a gap would form. The onlydecisive factor is that again no layer of solder 7 is provided in theregion of the reaction space 5. By analogy with the other exemplaryembodiments, here too, the catalyst material may be introduced in thereaction space 5 in the form of a loose fill or pellets instead of thecoating.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

What is claimed is:
 1. A process for producing a compact catalyticreactor, said process comprising: forming respective reaction spaces andheat-transfer spaces, by stacking at least partially structured platesalternately one on top of the other; introducing catalyst material intothe reaction spaces; providing a layer of solder at least in an edgeregion of the plates, but not in regions provided with catalystmaterial; and applying heat and pressure to the plates such that saidlayer of solder bonds the plates to form a catalytic reactor.
 2. Theprocess according to claim 1, wherein the catalyst material isintroduced into the reaction spaces by one of: in the form of a loosefill, in the form of pellets, or by coating the plates.
 3. The processaccording to claim 1, wherein metal foils or corrugated sheets are usedas plates.
 4. The process according to claim 1, wherein solder isintroduced by one of: a coating of the plates and in the form of a layerof solder.
 5. The process according to claim 4, wherein said step ofproviding a layer of solder comprises: forming clearances in the layerof solder in a region of the reaction spaces having catalyst material.6. The process according to claim 1, wherein the plates facing theheat-transfer space are coated completely with a layer of solder.
 7. Theprocess according to claim 1, further comprising: bending the platesover at edges thereof before said stacking step; and providing at leastthe bent-up edge regions with a layer of solder.
 8. The processaccording to claim 1, further comprising: providing an unstructuredintermediate plate between respective structured plates; and applyingthe layer of solder only to the intermediate plates, on both sides. 9.The process according to claim 8, wherein the layer of solder is removedon the surface of the intermediate plate facing the reaction spacefilled with catalyst material.
 10. The process according to claim 8,wherein the intermediate plate has a depression and/or clearance, forforming a defined gap in at least one of the regions of the reactionspace and the heat-transfer space.